Preparation Of Shell-core Structured Magnetic Adsorbent For Cu(Ⅱ) And Pb(Ⅱ) Removal From Aqueous Solutions

Heavy metals are important contaminants in the liquid wastes of large number ofindustries. Heavy metals into the environment can not be degraded，they are highly toxicand can cause a variety of negative effects on human health even at low dosages.Adsorption is an attractive approach in groundwater and drinking water treatment, due tohigh removal efficiency and without yielding harmful by-products. The manganese oxidesincluding MnO2have been reported to be effective adsorbents for metal ion removalbecause of their affinity in the adsorption process. However, masses of the manganeseoxides present relative small particle size and difficult recycling, which limit theirapplicability. Manganese oxide coated iron oxides with high magnetic permeabilityproduce a large adsorption capacity and overcome the problem of separation of manganeseoxides powder after water treatment. The research described here was designed to test theproperties of MnO2coated Fe3O4and MnO2coated Fe-Mn for removing copper and leadions from synthetic solutions.Adsorbents with Fe3O4and Fe-Mn respectively as magnetic core and MnO2as shellwas prepared by co-precipitation process. The adsorbents were characterized usingmultiple techniques. The TEM image indicated that Fe₃O₄/MnO₂and Fe-Mn/MnO₂werenanosized particles. X-ray powder diffraction （XRD） analysis showed that the magneticphase in Fe₃O₄/MnO₂and Fe-Mn/MnO₂were spinel magnetite. Fe₃O₄/MnO₂andFe-Mn/MnO₂have a highly specific saturation magnetization of54.7A·m2·kg-1and35.1A·m2·kg-1and a specific surface area of76.5m2·g-1and113.3m2·g-1.The properties of Fe₃O₄/MnO₂and Fe-Mn/MnO₂as adsorbents for removing copperand lead ions from synthetic solutions were investigated in a batch system. The results ofbatch sorption experiments suggested that the Fe₃O₄/MnO₂and Fe-Mn/MnO₂magneticadsorbents were effective for Cu²⁺and Pb²⁺removal from water, particularly at lowequilibrium concentration. The isotherm data was well fitted by Langmuir model. Themaximum adsorption quantities of Cu²⁺per gram Fe₃O₄/MnO₂and Fe-Mn/MnO₂in single component sorption systems were21.6and33.6mg·g-1at pH5.0, respectively. For Pb²⁺,they were142.0and261.1mg·g-1, respectively. The kinetics of Cu²⁺and Pb²⁺adsorptionconsisted of two phases: an initial rapid phase and a slower second phase. Thepseudo-second-order model was the best choice among all the kinetic models to describethe adsorption behavior of Cu²⁺and Pb²⁺with the two adsorbents. The Cu²⁺and Pb²⁺adsorption increased with increasing values of solution pH and was not significantlyaffected by the change of ionic strength. It can be concluded from adsorption isothermsand kinetics that chemical adsorption be predominant for the adsorption of metal ions onthe three adsorbents. The adsorption mechanism has been explained on the basis of twoadsorption ways of surface complexation and electrostatic adsorption.